Abortion Rates Down

From WaPo:

After years of holding steady, new Center for Disease Control data shows that the United States abortion rate has fallen to an all-time low. It dropped 5 percent between 2008 and 2009, the most recent years for which data is available, the largest decline in the past decade.

The big question for public health researchers is: Why? What was different in 2008, that might have lead to this downtick in abortions?

What’s the most reasonable explanation?